Why do Thunderstorms Often Occur on Summer Afternoons? Credit: NOAA National Severe Storms Laboratory / The Weather Prediction.com
Thunderstorm on May 26th, 2012 in Alliers, France
Thunderstorms are a weather phenomenon that occur and develop due to high amounts of moisture in the air along with warm air that is rising. These storms typically last less than thirty minutes and occur within a 15-mile radius. According to NOAA, in the United States nearly 100,000 thunderstorms occur each year, with ten percent of these storms becoming severe thunderstorms. Thunderstorms occur most often in the afternoon and evening of the spring and summer months, and bring with them thunder, lightning, heavy rain, and the potential risk for flash flooding.
A thunderstorm forms when warm moist air is unstable and begins rising. As this warm air rises the water vapor within the air cools and releases heat. Condensation then occurs as the air condenses creating a cloud, that then grows until it forms a towering cumulonimbus cloud. Ice particles within the cloud holding both positive and negative charges create lightning when leaders extend from these charges within the cloud. These negatively and positively charged particles within the cloud connect through a channel with the opposing charges of electricity rising up from the ground, creating a strong electric discharge. Lightning is followed by thunder after the lightning heats up the surrounding air causing it to expand rapidly. This expansion creates sound waves that make a loud cracking sound after the lightning strikes.
Thunderstorms occur more often in the afternoon and evening because in order for there to be high amounts of moisture in the air along with warm rising air, there must be instability in the atmosphere. During the warmer months the humidity is much higher. On days with less clouds in the sky temperatures can also rise to very high values. Because of this daytime heating throughout the day, the late afternoon and evening hours are when radiational heating and instability are at their highest points, and thus there is a steep temperature gradient between the mid-levels and the Boundary Layer. This daytime heating is often strong enough to completely overcome significant capping inversions, thus triggering Convective Available Potential Energy or CAPE that can spur up even severe thunderstorms. The intense heating that can occur during the daytime of the spring and summer months is very conducive for afternoon and evening thunderstorms. As the summer comes to a close, be sure to be aware of the potential for afternoon thunderstorms and the risks that come along with them.
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©2019 Weather Forecaster Christina Talamo